1. Field of the Invention
The invention is based on a device for restoring a rotary member to a defined basic position, in particular for restoring a throttle valve shaft, which carries a throttle valve for controlling the combustion air of an internal combustion engine, to an emergency-air position of the throttle valve, as generically defined by the preamble to claim 1.
2. Description of the Prior Art
One known restoring device, when used for a throttle valve, serves to return the throttle valve to a defined position of repose, the so-called emergency-air position or emergency-operation position, if the drive mechanism for the throttle valve fails; in this position, a minimal throttle valve opening for delivering combustion air to the engine is assured, so that the engine will still run smoothly while idling or at minimal load. Because of tolerances in the cams and the imprecision of bending the bent-away spring legs of the clamp spring, there is a certain play in the basic position, in which position the fixation cams and slaving cams are side by side, radially offset and approximately coincident, and this play leads to a freedom of rotation of the throttle valve that makes it impossible to provide precise regulation in this area.
In a known restoring device for restoring a throttle valve, disposed in a throttle valve neck in internal combustion engines (German Patent Disclosure DE 197 35 046 A1), oblique stop faces are provided in order to suppress the rotary play between the cams in the basic position of fixation cams and slaving cams. The spring leg bent away on one end of the clamp spring is retained on one side on the oblique stop faces, and the spring leg bent away on the other end of the clamp spring is retained on the other side on the level stop faces extending parallel to the axis of rotation, by fixation cams and slaving cams. Because of the oblique stop faces, the spring leg is braced on the two oblique stop faces with half the spring force each and as a result adjusts the rotatable slaving cam against the stop formed by the spring leg on the other side of the fixation cam or slaving cam.
For attaining a freedom of rotation in the slaving cam in the emergency-air position between a spring leg of the clamp spring and a stop face on one of the cams, it has already been proposed (German Patent Disclosure DE 100 13 917.5), that a compensation spring be provided, with a defined spring force oriented counter to the prestressing force of the clamp spring. The compensation spring, made as a stamped part, is fixed on one of the cams, thus placing one spring leaf in front of a stop face of the cams, which with its free end of the leaf rests with prestressing on a spring stop, disposed at a spacing from the stop face, that limits the spring travel of the spring leaf.